1. Technical Field
The present invention relates to a lighting device and an electronic device.
This application claims priority from JP-A-2009-204434, filed on Sep. 4, 2009 and JP-A-2009-208982, filed on Sep. 10, 2009, the content of which is hereby incorporated by reference.
2. Related Art
A front light is known which is a lighting device disposed on the display surface of a liquid crystal panel and illuminating the display surface. In general, the front light is used for reflection type display panels. When there is sufficient outside light, the light is turned off and the front light becomes a transparent plate to transmit the front light in a transparent plate state to thereby perform reflection display by the outside light in many cases. Therefore, the front light is frequently used for penetration type display panels. It is said that power consumption can be reduced rather than back light that is turned on irrespective of the existence of outside light.
For example, JP-A-2007-17720 discloses a front light having, on a reflection type liquid crystal display device, an organic EL device as a light source having an anode containing a transparent conductive material, such as ITO (Indium Tin Oxide), an organic EL layer disposed on the anode, and a cathode (reflective film) containing metal, such as aluminum, disposed on the organic EL layer.
FIG. 32 is an equivalent circuit diagram showing the electrical structure of a former front light. A front light 501 has an anode wiring 503 connected to an anode of a direct current power supply 502 and a cathode wiring 504 connected to a cathode thereof. The anode wiring 503 and the cathode wiring 504 are branched into a plurality of wiring lines and a plurality of light emitting elements 505 that are connected in parallel and emit light by a forward direction current are provided between each anode wiring 503a and each cathode wiring 504a. 
However, the former front light has a problem in that since the organic EL device has been used as the light source, it has been difficult to secure sufficient life. In detail, organic EL materials are materials that are being developed and have a problem in that the luminance life is short.
Moreover, due to a structure such that, in both the cases where the light is ON and OFF, the display surface is observed through the front light itself, the size (lighting area) of the organic EL device having a reflective film (cathode) and serving as a light shielding portion has been made small in such a manner as not to influence display. Therefore, in order to obtain an expected luminance, a high current needs to be applied, which increases the temperature of the organic EL device, resulting in a problem in that the organic EL device deteriorates. More specifically, there has been a problem in that it has been difficult to suppress deterioration of light emitting elements.